Ferromagnetic materials on the basis of nickel ferrite or nickel-zinc ferrite



United States Patent 3,509,058 FERROMAGNETIC MATERIALS ON THE BASIS OF NICKEL FERRITE 0R NICKEL-ZINC FERRITE Georges Estival, Argenteuil, Val-dOise, and Marc Monneraye, Aubervilliers, Seine-St.-Denis, France, assignors, by mesne assignments, to US. Philips Corporation, New York, N.Y., a corporation of Delaware No Drawing. Filed Aug. 15, 1967, Ser. No. 660,605 Claims priority, applicatio7n France, Aug. 23, 1966,

Int. C1. 0045 35/28, 35/30 US. Cl. 25262.62 2 Claims ABSTRACT OF THE DISCLOSURE This invention relates to ferromagnetic materials on the basis of nickel ferrite or nickel-zinc ferrite.

It is known that certain representatives of these classes of materials are very suitable for manufacturing magnetic cores used at high frequencies, more particularly frequencies higher than 1 mHz. It is important that the initial permeability of these cores should vary with temperature to the least possible extent in the range between 20 C. and 70 C. or at least between 20 C. and 55 C. In connection therewith it has previously been suggested to decrease the temperature factor of the initial permeability in the said range of temperatures by adding to the relevant ferrites small amounts, for example, from 0.4 to 4.0 mol. percent of cobalt oxide CoO (see French patent specification No. 1,185,406).

The temperature factor F of the initial permeability is a magnitude which is obtained by dividing the temperature coefficient T of the initial permeability (m) by this permeability, that is to say Mol. percent Fe O 47-49 NiO 18.25-28.75

ZnO 24-32 v.0. 0.2s 0.7s

Mixed ferrites according to the invention are distinguished by the following combination of favourable properties:

(l) A minimum, and hence optimum, value for the quotient tan fi/ of the initial permeability and the loss factor in a maximum range of frequencies;

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(2) A minimum value for the temperature factor F of the initial permeability, while the value of the differential quotient d /dT does not vary its sign in the temperature range considered;

(3) insensitivity to magnetic impact effect" such that the properties of the material as a whole are not substantially affected in an irreversible manner by the action of a strong constant magnetic field or a demagnetising alternating magnetic field.

Ferrites according to the invention have a composition located within the range of compositions which is characterized by the following relative amounts of the constitutive metal oxides:

Mol. percent Special attention is drawn to the fact that the content of ferric oxide, Fe O must at any rate not be higher than 50 mol. percent and preferably even not higher than 49.8 mol. percent. It is also mentioned that for comparatively low values of the molecular ratio NiOzZnO a fairly high content of ferric oxide, Fe O within the specified range of concentrations is advantageous. If, for example, the value of the molecular ratio NiOzZnO is approximately 1 to 3, the optimum content of the ferric oxide lies at approximately 49.4 to 49.9 mol. percent. If the value of the molecular ratio NlO'SZIlO is comparatively high, the content of the ferric oxide within the specified range of concentrations is less critical.

The manufacture of materials according to the invention is, broadly speaking, similar to that which is commonly used for known nickel ferrites and nickel-zinc ferrites. Consequently, a mixture of compounds of iron, nickel, cobalt, vanadium and possibly zinc (oxides of these metals and/ or compounds which can change to the corresponding metal oxides at the sintering temperature) is sintered at a temperature between 1,000 C. and 1,400

C., it being possible for the said compounds to be replaced wholly or in part by reaction products of two or more of said metal oxides which have been previously formed.

Table II indicates the values for the initial permeability, those for tan a/ hence for the quotient of the loss factor and the initial permeability, and those for the temperature factor F of the initial permeability for a series of materials 1 to 14, the chemical compositions of which are specified in Table I.

The electromagnetic losses have invariably been measured on toroidal magnetic cores each surrounded by a coil having a number of turns depending on frequency. No correction was made for the losses occurring in the coil itself, so that the loss values specified in Table II are greater than those of the ferrite bodies concerned.

TABLE I Mol percent Molecular ratio N 10: Material F6203 NiO ZnO C00 V205 ZnO TABLE II tan FX in the temperature range 5 4 v m X10 at a hequenc (in rnHz.) of between 1. 5 2 5 10 Id 30 40 50 20 and 20 and 20 and 70 C. 60 C. 55 0.

Material The material 1 is a mixed ferrite of nickel and zinc having a small shortage of iron (that is to say an iron content lower than equivalent to 50 mol. percent of Fe 0 Including 0.9 mol. percent of C00 in this material yields the material 2 of which the initial permeability and the loss factors at the various measuring frequencies are approximately equal to the corresponding values of the material 1, but of which the temperature factor F of the initial permeability ,u between 20 C. and 70 C. is distinctly lower and hence better. Including in the material 2 a small amount (0.30% by weight) of V 0 which is added as such or in the form of ammonium vanadate to either the initial mixture or the ground presintered product, yields the material 3 of which all the magnetic properties which are important in the present connection are distinctly superior to the corresponding properties of the 10 minutes.

TABLE IV tan 5x106 lrior to the magnetic ifter the magnetic m impact treatment impact treatment 1. 5 mHz. 40 42. 5 2 mHz. 43 45 From these figures it appears that the material 7 is also highly resistant to magnetic impact effect. The same is true of the material 8 of Table I (NiO:ZnO=l.9) as may mammal u be seen from Table V which relates to the manner in In f to h the reslstwlty Qg which this material reacts to a magnetic impact treatment magnetlc Impact effect 15 {ntlmately collnected Wlth the by means of a magnetic constant field of 25 oersteds for iron content chosen, three different materials were manu- 1O minut6s factured having the same molecular ratios NiOzZnO, TABLEV C00 contents and V 0 contents, but two materials of which have higher iron contents than correspond to 50 2 Prior to the magnetic After the magnetic L percent of 0 I: impact treatment impact treatment The three materials concerned were subjected to the 2 mHz. 35 33 action of a magnetic constant field having a strength of 8 $52: $1 four times the coercive force of the material concerned. 15 Indie. 135 160 Magnetic cores which, prior to magnetisation, differed in loss values to the least possible extent were compared 2 are Obtained with materials having with one another. The magnetic impact eifect was obp t ly high Values the molecular ratio NiOZZnO. tained by subjecting the relevant magnetic cores to the Table V relates to the matel'lal 11 of Table I having 3 action of a magnetic constant field of 20 oersteds for 5 molecu ar ratio N1O:ZnO 0f Which ial w s minutes. sub ected to the action of a magnetic constant field of Table III shows the influence of the magnetic impact 35 oersteds 0 minutes. eitect on the materials 4, 5 and 6, the material 4 having TABLE W a chemical composition similar to that of the material 3, tan 5 P t th I I 0 104;, nor -0 emagnetic After the ma neti but which was manufactured by a slightly diiferent m X a Impact treatment impact treatglentc method, while the iron contents of the materials 5 and 30mm 230 6, as shown in Table I, are higher than that correspond- 40 m: 279 ing to 50 mol. percent of Fe O 50 385 892 TABLE III tan 6 T X106 at afrequency (in mc./s.) of- Priort-othe Afterthe Pi -t 1-, magnetic magnetig R lfl ag et i iiiiiiviiii 11 pa nmpac rec in impact impact Rise in im act im t Material t; treatment tieatment percent treatment treatment percent treat-iiient treat ii gnt gi c eiit 4 73 5s 5s 0 5 n m e 82 30 it a it a: 332, 6 50 87 114 31 33 138 286 107 As will be apparent from Table III, the loss factors of the materials 5 and 6 are very sensitive to the mag- The lower limit of the iron content is determined by the influence of this content on the temperature factor.

netic impact treatment, whereas those of the material 4 75 Thus the material 9 of Table I (Fe O =49 2 t cent) has a temperature factor F of the initial permeability of 73x10 between 20 C. and 55 C. A material distinctly sensitive to magnetic impact effect, as may appear from Table VII following hereinafter.

TABLE VII g- X10 at a frequency (in mHz.) of- Prior to the After the Prior to the After the magnetic magnetic magnetic magnetic impact impact Rise in impact impact Rise in Material n treatment treatment percent treatment treatment percen is concerned having a molecular ratio NiO:ZnO of 1.55, which is a comparatively low value. As previously mentioned, the iron content is less critical for a comparatively high value of the molecular ratio NiO:ZnO. Thus, for example, the materials 10, 11 and 12 of Table I (molecular ratios NiOzZnO of 10.5 to 12), are all of good quality on the standards used in this connection, although the iron content expressed in mol. percent of Fe O varies between 48.6 and 49.3. By the way it is mentioned that for the material 12, in order to achieve a temperature factor F of approximately zero between 20 C. and 60 C., a change of sign of the dilTerential quotient d/J/dT in this temperature range had to be taken into the bargain by way of exception. This shows again that the effect resulting from the combination of a shortage of iron and an addition of small amounts of cobalt oxide and vanadium oxide invariably occurs, irrespective of the value for the molecular ratio NiOzZnO (at least insofar this value is not lower than approximately 0.8).

The materials 13 and 14 of Table I have, as the previously mentioned materials 5 and 6 of this table, iron contents equivalent to more than 50 mol. percent of Fe203. Although their chemical compositions do not differ, these materials have different values for the initial permeability because the temperature treatment used for the manufacture of the one material diflfered slightly from that used for the manufacture of the other material. However, due to both materials including an excess of iron (and hence their iron contents being higher than correspond to 50 mol. percent of Fe O both are also M01. percent Fe O 48-50 NiO 22-49 ZnO 047 2. A material for magnetic cores as claimed in claim 1 wherein the Fe O content is 49.2 to 49.8 mol. percent.

References Cited UNITED STATES PATENTS 2/1956 Crowley et al. 252-6256 5/1956 Piekarski 252-6262 TOBIAS E. LEVOW, Primary Examiner R. D. EDMONDS, Assistant Examiner US. Cl. X.R. 252-6256 

